This invention relates to slag, specifically to that used in the steel-making industry.
A slag is present on the top of the melt in a metallurgical furnace or vessel. The main function of the slag is to combine with unwanted impurities from the melt so that they can be separated from the melt. It also tends to prevent the melt from picking up gases from the furnace atmosphere.
It is known that the so-called basicity ratio of the slag is important in steel-making. The basicity ratio is defined as the ratio of basic oxides to acidic oxides.
One measure of the basicity ratio (B) is defined thus:
  B  =                    %        ⁢                                  ⁢        CaO            +              %        ⁢                                  ⁢        MgO                            %        ⁢                                  ⁢                  SiO          2                    +              %        ⁢                                  ⁢                  Al          2                ⁢                  O          3                    
Other, sometimes more useful, measures of the basicity ratio have been proposed (see Turkdogan E. T. The Fundamentals of Steelmaking; The Institute of Materials (1996)). Such measures may be expressed thus:
            B      LF        =                            %          ⁢                                          ⁢          CaO                +                  1.4          ⁢          %          ⁢                                          ⁢          MgO                                      %          ⁢                                          ⁢                      SiO            2                          +                  0.6          ⁢          %          ⁢                                          ⁢                      Al            2                    ⁢                      O            3                                or      V    =                  %        ⁢                                  ⁢        CaO                    %        ⁢                                  ⁢                  SiO          2                    
Virgin slag compositions are slag compositions which are brought into contact with the melt at the commencement of the steel making process. The values for basicity ratios, as defined above, are typically above 2 for the so-called “virgin” slag compositions.
Care must be taken when using and referring to the basicity ratio as there are many ways of defining the basicity (see, for example, Sommerville, I. D. and Yindong Yang; The AusIMM Proceedings, pp. 71, Vol. 36 No. 1; 2001).
Furnaces used in the steel industry, for example Basic Oxygen Furnaces (BOFs), Electric Arc Furnaces (EAFs) and Ladle Furnaces (LFs) are metal vessels which have a refractory lining to hold the molten metal. The refractory materials are chosen to withstand the extreme temperatures to which they are subjected. It is important for reasons of economy and efficiency that damage to the refractory materials is minimised. Damage to such refractory materials is controlled by, inter alia, the basicity and by MgO saturation levels.
Many industries seek to gain extra benefit out of production processes by reclaiming waste materials. Such reclamation may take the form of recycling unused or partially used materials or the reclamation of say energy in the form of heat by combusting waste materials. One such industry is the paper production industry where the by-product, waste paper pulp or sludge, is often burnt. The product of the so-combusted waste is known as combustion ash.
Combustion ash from the paper production industry is typically a fine powder substantially composed of calcium oxide, silicon dioxide, aluminium oxide, magnesium oxide and iron oxide. Small amounts of other metallic oxides and chlorides are also usually present. Because of the physical composition and state of combustion ash it has heretofore had limited economic use and is typically land-filled. In many parts of Europe, at least, a charge is levied for the disposal and, say, land filling of industrial waste.
It is an object of the present invention to provide a cheap source of virgin slag, whilst providing an economic sink for combustion ash, thereby reducing land-fill and producing a further income stream. It is a further object of the invention to provide a so-called “artificial” slag made at least partially from waste materials. It is a yet further and more specific object of the invention to provide an artificial slag from waste materials which causes no, little or not excessive damage to the refractory materials used in steel-making processes.